1. Field of the Invention
This invention relates to a novel cyclo-olefinic random copolymer. More specifically, the invention has for its object the provision of a cyclo-olefinic random copolymer having excellent transparency, thermal stability, heat aging resistance, chemical resistance, solvent resistance, dielectric properties and mechanical properties and a narrow molecular weight distribution and a narrow composition distribution.
This invention also relates to a novel olefinic random copolymer. More specifically, the invention has for its object the provision of an olefinic random copolymer containing a carbon-carbon unsaturated bond in its side chain which has excellent transparency, thermal stability, heat aging resistance, chemical resistance, solvent resistance, dielectric properties and mechanical properties and a narrow molecular weight distribution and a narrow composition distribution.
This invention further relates to a process for producing a cyclo-olefinic random copolymer by copolymerizing an alpha-olefin and a cyclo-olefin in the presence of a highly active polymerization catalyst. More specifically, the invention relates to a process for producing a cyclo-olefinic random copolymer which comprises copolymerizing an alpha-olefin and a cyclo-olefin in the presence of a catalyst comprising a specific transition metal compound and an aluminoxane.
2. Description of the Prior Art
Known processes for producing cyclo-olefinic copolymers by copolymerizing alpha-olefins such as ethylene and cyclo-olefins involve the use of titanium-containing catalysts comprising titanium compounds and organoaluminum compounds or vanadium-containing catalysts comprising vanadium compounds and organoaluminum compounds.
In a copolymerization process using a titanium-containing catalyst, a cyclo-olefin has lower reactivity than an alpha-olefin such as ethylene and the copolymerization efficiency is low. In order, therefore, to expect production of a copolymer of the cyclo-olefin with the alpha-olefin, it is necessary to add the cyclo-olefin in a large quantity to the polymerization system. The presence of a large quantity of the cyclo-olefin reduces the activity of the catalyst and may result in a decrease in the molecular weight of the resulting copolymer. It is difficult therefore to obtain a high-molecular-weight copolymer. Moreover, this process has the defect that side-reactions such as the ring-opening polymerization of the cyclo-olefin tend to occur, and the resulting polymer has a broad molecular weight distribution. On the other hand, in a copolymerization process using a vanadium-containing catalyst, the copolymerization efficiency of the cyclo-olefin is higher than in the case of using the titanium-containing catalyst and the resulting copolymer has a narrow molecular weight distribution. But it has the defect that the polymerization activity is generally very low.
Catalysts comprising transition metal compounds and aluminoxanes are proposed as highly active polymerization catalysts for olefins in, for example, Japanese Laid-Open Patent Publications Nos. 19309/1983, 95292/1984, 35005/1985, 35006/1985, 35007/1985 and 35008/1985. Of these, Japanese Laid-Open Patent Publications Nos. 19309/1983, 35005/1985, 35006/1985, 35007/1985 and 35008/1985 describe that these catalyst systems can be applied to the copolymerization of ethylene with other alpha-olefins. With regard to the production of cyclo-olefinic copolymers, Japanese Laid-Open Patent Publication No. 221206/1986 discloses a catalyst comprising a transition metal compound and an aluminoxane with regard to the production of a copolymer of an alpha-olefin and a cyclo-olefin. This catalyst, however, has low polymerization activity, and is difficult of giving the copolymer in good yields.
It is generally known that by using Ziegler-type catalysts comprising a combination of titanium or vanadium compounds and organoaluminum compounds, binary copolymers of ethylene with cyclo-olefins or ternary copolymers of ethylene, alpha-olefins such as propylene or 1-butene and cyclo-olefins are obtained. However, no example has been known in which an alpha-olefin having 3 to 20 carbon atoms was copolymerized with a cyclo-olefin in the absence of ethylene with a Ziegler-type catalyst. Naturally, no such copolymer has been reported so far.
Polycarbonate, poly(methyl methacrylate) and polyethylene terephthalate have been known as synthetic resins having excellent transparency. For example, polycarbonate is a resin having excellent thermal stability, heat aging resistance and impact strength in addition to excellent transparency, but have the disadvantage of being inferior in chemical resistance and susceptible to attack by strong alkalies. Poly(methyl methacrylate) is susceptible to attack by ethyl acetate, acetone and toluene, is swollen in ether and has low thermal stability. Polyethylene terephthalate has excellent thermal stability and mechanical properties, but is susceptible to attack by strong acids or alkalies and liable to undergo hydrolysis.
Many polyolefins widely used as general-purpose resins have excellent chemical resistance, solvent resistance and mechanical properties, but poor thermal stability. Moreover, they have poor transparency because of their crystalline nature. Generally, the transparency of polyolefins is improved by adding a nucleating agent and thereby finely dividing their crystalline structure, or by quenching them to stop growth of crystals. The effects of such techniques, however, have not proved to be entirely satisfactory. Rather, the addition of a third component such as a nucleating agent is likely to reduce the inherent excellent properties of the polyolefins. The quenching method requires a large-sized apparatus, and with a reduction in crystallinity, the polyolefins are likely to be degraded in thermal stability and rigidity.
With regard to the copolymerization of ethylene with bulky comonomers, U.S. Pat. No. 2,883,372, for example, discloses a copolymer of ethylene and 2,3-dihydrodicyclopentadiene. This copolymer has an excellent balance between rigidity and transparency, but poor thermal stability because its glass transition temperature is about 100.degree. C. A copolymer of ethylene and 5-ethylidene-2-norbornene has similar defects.
Japanese Patent Publication No. 14910/1971 proposes a homopolymer of 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydro-naphthalene. This polymer, however, has poor thermal stability and heat aging resistance.
Japanese Laid-Open Patent Publication No. 127728/1983 proposes a homopolymer of 1,4,5,8-dimethano-1,2,3,4,4a,5,8,8a-octahydronaphthalene or a copolymer of the above cyclo-olefin and a norbornene-type comonomer. It is clear from this patent document that these copolymers are ring-opened polymers. These ring-opened polymers have poor thermal stability and heat aging resistance because they contain an unsaturated bond in the main polymer chain.
Japanese Laid-Open Patent Publications Nos. 168708/1985, 98780/1986, 115912/1986, 115916/1986, 120816/1986, 95906/1986 and 95905/1986 disclose that olefinic random copolymers of ethylene and specific bulky cyclo-olefins have a good balance in thermal stability, heat aging resistance, chemical resistance, solvent resistance, dielectric properties and mechanical properties while having transparency, and exhibit excellent performance in the field of optical materials such as optical memory discs and optical fibers. These copolymers contain ethylene copolymerized therein, and in order to impart good thermal stability, a large amount of a cyclo-olefin must be copolymerized. Reaction of such copolymers with maleic anhydride or the like to impart polar property to these copolymers usually requires the use of peroxides. This causes cleavage of the main chain and results in a reduction in molecular weight. It is desired therefore to provide olefinic random copolymers which in spite of a low cyclo-olefin content, have excellent thermal stability and can be modified without using peroxides.